The Medical Practice Study has reported rates of adverse events discovered in a sample of 31,000 hospitalizations in 1984 in New York. An adverse event is a disabling injury caused at least in part by medical management. Those estimates were based on a protocol that called for duplicate physician reviews on 7700 medical records. As part of this process, the Study identified 1600 cases characterized by physician disagreement on the presence -of a causal connection between the injury and the medical care. Proposed no-fault alternatives to litigation for compensating injured patients have not assessed empirically the issues of clinical decision-making under an administrative system that determines eligibility and responsibility for patient compensation. This proposal seeks to describe and assess the extent and nature of reviewer disagreement about adverse events, and to address the implications of these empirical findings for current proposals for no-fault patient compensation systems.